The invention relates to methods and systems for remediating contaminated soil, and more particularly to a methods and systems for volatilizing contaminants in the soil and effectively and efficiently removing same therefrom.
Systems for conducting fluid through a soil stack are known. U.S. Pat. No. 4,139,321 describes a rock channel heat storage method involving conduit connections provided within a rock-filled channel. The conduits are used to conduct fluid through the rock pile to either absorb or disperse thermal energy. Soviet Patent 837,997 describes a method for the thermal treatment of embankment soil. A main hold 3 receives heated combusted gas and directs same into spiral holes 5 which are vented through valves 8. U.S. Pat. No. 4,036,285 describes an arrangement to control heat flow between a member and its environment including conduit members which conduct heat transfer fluid underground. Other patents which show devices for conducting fluid through a soil stack include U.S. Pat. Nos. 123,384; 2,332,227; 2,332,227; 3,105,134; 3,564,862; 3,935,900; 5,449,113; Soviet Union 600,262; Soviet Union 996,662; Fed. Rep. Germany 2,706,740
Systems for removing contaminants from the ground are also known. For example, U.S. Pat. No. 4,982,788 removes contaminants from the ground by circulating air between two substantially parallel wells and by removing the vapors of the organic compounds from the circulated air using at least one of a condenser and a demister. U.S. Pat. No. 5,011,329 relates to in situ decontamination by injecting a hot gas into boreholes formed in a contaminated soil area. A method is also provided in U.S. Pat. No. 5,018,576 for in situ decontamination of contaminated subsurface areas by injection of steam into injection wells and withdrawing of liquids and vapors from the wells under sub-atmospheric pressure.
Systems have also known for removing contaminants from soil piles or soil stacks. U.S. Pat. No. 4,973,811 relates generally to in situ decontamination of soil using radio frequency induction heating. In U.S. Pat. No. 5,035,537, soil, porous rock, and similar contaminated materials are gathered, dispersed uniformly on a horizontal surface, and treated with an emulsifying agent.
U.S. Pat. No. 5,067,852 relates to a method and apparatus for removing volatile contaminants from contaminated soil which has been stacked onto a first vapor-tight liner. A first set of air distribution pipes disposed within the soil stack each of which has an opened end, a closed end, and a plurality of perforations located in the body of the pipes. An air stream is introduced into the open end of the distribution pipes and exits the distribution pipes through the perforations and into the contaminated soil stack. The air flows from the distribution pipes, through the contaminated soil, and volatilizes contaminants within the contaminated soil. The air flow from the distribution pipes employees a gravel filter medium to prevent the perforations in the distribution pipes from clogging. The volatized vapor created as a result of the induced air flow is carried by the air flow through the soil, and is exhausted from the soil. The volatilized vapors exiting the soil stack are disposed of through an external vapor treatment system. A second vapor-tight liner is placed over the soil stack to creating an impervious enclosure between the respective first and second liners, which are typically formed of a polyethylene film. In order to avoid melting of the first and/or second liners, the temperature of the soil stack would have to be maintained below the melting temperature of the respective liners.
U.S. Pat. No. 5,213,445 and U.S. Pat. No. 5,340,236 are directed to a similar process to US '852 except that they provide a recirculating system which destroys the contaminant phase and returns heated decontaminated air to the air distributions pipes. The air heating unit, which is located outside of the soil stack, heats the air to temperature of between 275 and 300 degrees F.
The above-described methods and systems, which are incorporated herein by reference, have a number of drawbacks. They are closed loop systems which recirculates a substantial portion of the heated air after the contaminants are burned or removed. Recirculation of air through heaters reduces oxygen in the air stream thereby reducing the effective level of volatilization. These systems of US '852, US '445 and US '236 make use of a vacuum to encourage contaminants to achieve vapor phase which has proven to be an ineffective approach for affecting remediation. As previously stated, the temperature of the volatizing air must be maintained below the melting temperature of the sealing member in order maintain its structural integrity. The above prior art systems are designed to move the vaporized contaminants through the soil stack into the space thereabove surrounded by the flexible sealing member. Therefore, the soil cannot be packed down to maintain the structural integrity of the soil stack without adversely effecting the efficiency of the remediation process.